The 2,6-difluorobenzonitrile is a useful intermediate in various industries, particularly in the agricultural chemicals industry. In making the intermediate, numerous processes have been employed. UK Patent 2 142 018 B to Ishihara Sangyo Kaisha Limited discloses reacting 2,6-dichlorobenzonitrile with potassium fluoride in the absence of solvent at 200.degree. to 450.degree. C. under pressure. More specifically, the Ishihara Patent discloses employing at least 21.5 kg/cm.sup.2 of pressure. In addition to not employing a solvent, the process disclosed by Ishihara does not employ a catalyst. Japanese Patent Publication #87-114,939, Derwent Publication #87-183186126 to Sumitomo Chem. Industries, discloses reacting a benzonitrile with an alkali metal fluoride and an alkaline earth metal fluoride in the absence of a solvent and at a temperature between 100.degree. to 250.degree. C.
Japanese Patent 90-004,580, Derwent Publication #83-05838K/03 to Dainippon Ink Chemical, discloses a process for preparing p-fluoronitrobenzene by reacting a mixture of KF and an alkali metal fluoride (other than KF) or an alkali earth metal fluoride with a crown ether catalyst and p-chloronitrobenzeneo. Japanese Patent Publication No. 89-1013,037, Derwent Publication. #89-059218/08 to Ihara Chemical Industries, discloses preparing a halogenated aromatic compound with an alkali metal fluoride using a mixture of catalysts. The mixture of catalysts comprises a quaternary ammonium salt and/or a quaternary phosphonium salt and a crown ether and/or a polyalkylene glycol.
U.S. Pat. No. 4,226,811 to Bayer Aktiengesellschaft claims a process for preparing an aromatic ring-fluorinated compound by reacting a substituted chlorobenzene with potassium fluoride in the presence of a crown ether catalyst and a solvent. U.S. Pat. No. 4,978,769 to Bayer Aktiengesellschaft claims a process for preparing an aromatic fluorinated compound by nucleophilic exchange between an educt, such as 2,6-difluorobenzonitrile and KF in the presence of a phase transfer catalyst and a salt of a metal of main groups 3 to 5 of the periodic table of elements and of sub-group elements. Examples of such salts could include chromium salts (CrCl.sub.3 x6H.sub.2 O), iron salts (FeCl.sub.3), cobalt salts (CoCl.sub.2 x6H.sub.2 O), zinc salts (ZnCl.sub.2) and antimony salts (SbCl.sub.3).
U.S. Pat. No. 3,300,537 to Bennett which was assigned to The National Smelting Company discloses a process for converting halogen aromatic rings that do not contain an activating group such as nitro to a fluorinated aromatic compound. This reaction is conducted with a dry alkali metal fluoride at very high reaction conditions of between 300.degree. C. to 700.degree. C. without using a solvent or catalyst at high pressures.
In view of the previous process, it is highly desirable to have a process that would produce high yields, is environmentally preferred, but is economical. One of the problems with employing crown ether catalyst as described above is that they are extremely expensive, thereby making the processes not economical for commercial production.